1. Field of the Invention
The present invention relates to a medical manipulator for actuating a distal-end working unit on the distal end of a joint shaft with a motor that is energized by a controller, and more particularly to a medical manipulator in which a motor for actuating a distal-end working unit is feedback-controlled based on a comparison of angular displacement of the motor and an operation command value.
2. Description of the Related Art
When performing an endoscopic surgery (also called laparoscopic surgery), it is customary to form a plurality of incisions in the body surface of the patient, insert trocars (tubular instruments) into respective incisions as instrument passage ports, and introduce distal ends of forceps having shafts through the respective trocars into the body cavity to perform a surgical operation on an affected part of the body. Working units such as a gripper for gripping a living tissue, scissors, the blade of an electric scalpel, etc., are mounted on distal ends of the forceps.
An endoscopic surgical operation performed with forceps requires the surgeon to be trained in advance, because the working space in the body cavity is small and the forceps need to be operated using the trocars as fulcrums. Since forceps that have been used heretofore lack joints in the working unit on the distal end thereof, such forceps have a small degree of freedom, and the working unit can be operated only on an extension of the shaft. Therefore, cases that can be handled under the usual training practice for endoscopic surgery are limited to a certain range. The surgeon needs to be trained and highly skilled in order to be able to perform endoscopic surgery on various other cases not within this limited range.
Attempts have heretofore been made to improve conventional forceps and to develop a forceps having a plurality of joints in a working unit thereof (see, for example, Japanese Laid-Open Patent Publication No. 2004-105451). The manipulator disclosed in Japanese Laid-Open Patent Publication No. 2004-105451 comprises a manually operable operating unit, and a working unit replaceably mounted on the operating unit. The disclosed manipulator is free of the limitations and difficulties of conventional forceps, can be operated easily to perform surgical techniques, and can be applied to a wide variety of surgical cases. The manipulator can be used to perform various surgical techniques by replacing the working unit with working units of different types.
The manipulator includes a motor for moving the working unit, and a controller for measuring the angular displacement of the motor with an angle sensor, comparing a signal representative of the measured angular displacement with an operation command value, and controlling the motor through a negative feedback loop based on the result of the comparison. The motor actuates a distal-end working unit mounted on the distal end of a joint shaft through a power transmitting member such as a wire.
A medical robot system has been proposed for actuating such a manipulator via a robot arm (see, for example, U.S. Pat. No. 6,331,181).
In the manipulator described above, the controller compares a signal representative of the measured angular displacement with an operation command value, and controls the motor through a negative feedback loop based on the result of the comparison. The feedback control process makes it possible to operate the distal-end working unit accurately according to the operation command value.
However, if the feedback loop becomes accidentally broken in some way, the feedback control process fails to operate normally. Particularly, if a feedback route from the sensor to a subtracting point is broken, then the feedback loop changes into an open loop, and the controller fails to supply a feedback signal depending on the operation command value, so that the distal-end working unit could possibly operate unexpectedly.
Consequently, the signal line for transmitting the signal from the angle sensor should desirably have a highly reliable construction. The manipulator should also incorporate some means therein for judging whether the feedback system is malfunctioning or not, in preparation for unforeseeable situations. It is desirable that the malfunction judgment be carried out without adversely affecting the surgical operation being performed using the manipulator.